Pallets are widely used in the transportation and storage of goods, The goods (typically packaged in boxes or bags) are stacked on the pallet and bound thereto by straps or wrapping for shipment therewith as an integral unit. Loaded pallets are stored in warehouses either on the floor or in racks in adjacent single or multiple level layers.
Conventional pallets are usually made of wood. Wooden pallets offer good materials handling and stacking strength characteristics. The decreasing supply of readily available wood is raising the cost of such pallets, however, and such wooden pallets are heavy and bulky to transport.
The use of pallets made of corrugated paperboard and similar materials as a substitute for wooden pallets has gained limited acceptance for some applications. Such corrugated pallets are lightweight, relatively maintenance free and readily disposable or recyclable. They may be transported and stored in unassembled form for maximum space utilization when unloaded, and assembled on-site for loading. After usage, they can be broken down for disposal or recycling just like cardboard boxes and other corrugated products.
One kind of known corrugated pallet is illustrated by the structures shown in U.S. Pat. Nos. 2,446,914; 2,728,545; 3,464,371; and 3,477,395. Such pallets comprise a plurality of longitudinally extending elongated base members or stringers held in parallel, spaced relation by means of top and bottom rectangular decking sheets to form skids with open channels into which the tines of forklifts can be inserted for materials handling purposes. Other versions of such pallets, as shown in U.S. Pat. Nos. 3,131,856 and 3,683,822, add a degree of lateral stability by providing a plurality of laterally extending, parallel, spaced deck members or cross runners perpendicularly interconnecting the base members at axially spaced intervals to form a rectangular lattice structure. The deck members span the base members in elevated positions without floor contact between the base members leaving the fork channels unobstructed.
Though known corrugated pallets provide lightweight, inexpensive alternatives to conventional wooden pallets for some applications, their strength and rigidity under both static and dynamic loading is insufficient to permit widespread general usage for all types and distributions of goods. Base member constructions, such as shown in the '371 and '395 patents having wrapped, adjacent side-by-side thicknesses of fluted fiberboard material placed in vertical direction of corrugation, are not known to have been employed in criss-cross lattice type pallet structures such as shown in the '656 and '822 patents. Rather, the latter type corrugated pallets having perpendicularly interconnecting base and deck members have generally been formed from weak, relatively open core, support members. The skid type structures have no lateral support members at all; and the lateral members of the lattice type structures of not contact the floor between longitudinal members, so provide only suspension lateral weight supporting capabilities. Structures, such as the lattice shown in the '822 patent, are moreover prone to rocking instability, with the elevated cross ties being able to pivot out of the base members under dynamic loading.
No knows self-supporting pallet structures make adequate accommodation for four-way forklift tine entry into the pallet. The skid types represented by the '914, '545, '371 and '395 pallets, provide only two-way, front and rear entry into the spaced between the base members framed by the top and bottom sheets. The lattice types represented by the '656 and '822 patents provide the same two-way entry between the base members in the area below the deck members and, in addition, provide optional four-way access by means of cutouts or "pockets" made at floor level in the deck member (see, e.g., the pallets of Corpal Systems, Inc., Jacksonville, Fla.). Four-way entry is also provided in related but contained non-freestanding structures, such as shown in U.S. Pat. No. 3,666,165. However, such inherently weak, open core member structures lack strength at critical points and are subject to ripping at cuts made for fork tine insertion if the carried goods exceed the weight of cushions, textiles and similar light loads.
The strongest known corrugated pallets today have a load rating for a 4'.times.4' pallet of only 6,000-8,000 pounds under static loading. Such figures are only for careful uniform stacking of concrete blocks, however, and only for two-way addressable pallets. Under actual road transportation and warehouse stacking conditions, the strength of such pallets is considerably less. And, adding cutouts for four-way fork tine entry reduced the maximum strength load-carrying capability further.